Concentration quenching in fluorescent acene solutions

Measurements on the concentration dependence of the fluorescence intensity of dilute solutions of various acenes in n-hexane at 25°c show that the concentration quenching for benzene as a solute can be explained by simple collisional quenching. In solutions of naphthalene and anthracene the concentration quenching proceeds via an unstable excited complex resulting from the interaction of an excited and a non-excited molecule. The remarkable shape of the concentration curve of naphthalene is attributed to a contribution of the excited naphthalene complex to the total fluorescence intensity. The average life-time τ of the fluorescent electronic state, as calculated from the measurements, amounts to about 2×10−6 sec for benzene and 5×10−7 sec for naphthalene.